Tek DM44 Semiconductive PC Board

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Hi Mike,

well this problem I have seen with instruments used in industrial areas. As far as I can say about it is a problem of the dirt covering the boards. And, very interesting, it is most times NO VISIBLE dirt. I asked chemist from the local university, and he just nooded : He said that's often hapend due to certain sulfur and chloride chemicals that contaminate these boards in electronic devices (sorry I forgot about the full names of the chemicals).

In my situation this helped: thorough cleaning, comparable to the dishwasher method Jim Yanik descreibes in the newsgroup (use a little google time to find his articles).

Don't simply scrap the boards, some of the components (mostly LD110/111 chips) are real hard to get nowadays (at least here in europe)

hth, Andreas

Thanks Andreas,

My frustration selected the word "scrap", my apologies, I would never scrap these old DM44s I may "salvage" them, but only after I try one last time to search-out & eradicate these resistance phantoms.

Thanks for the reminder on cleaning out the dirt, absolutely a must do every time you "crack open" a new acquisition. I wish that was the solution in this instance. I have a shelf full of specialized chemicals & brushes for this.

The info from your chemist contact helps tremendously, sulfur & chlorine compounds can be conductive and they can migrate through certain mediums, like corrosion beginning at a battery terminal. I looks like this type of contamination is initially very localized and undetectable in QC yet migratory, and its only a matter of time before it migrates through the board composite until it contacts a couple of traces. This migration may take 20 years before it becomes a problem from what I'm gathering here.

I have a few old Teks (a 453, four 465s, a 475 & the cadillac 485) that are in beautiful condition. One 465 has one of my DM44s, the thing is, is that this 465 has serial number B320864, this is near the end of the production run for the 465 and I really want to keep it as it was optioned (with the DM44). I could go on eBay & find another "as is" 465/DM44 and swap out the boards, but I (as most techs) would feel defeated by taking this route to solve a problem. Yea, its personal. In the corporate world I would simply frizbee this problem board.

My last ditch effort will be to unsolder all the components in that area and begin ghostbusting. I did meet Bill Murray once a long time ago at a party. LOL

Thanks again, Mike

snipped-for-privacy@yahoo-dot-com.no-spam.invalid (Baytekk) wrote in news: snipped-for-privacy@corp.supernews.com:

Before you begin unsoldering,run the PCB thru your automatic dishwasher with Calgonite,and then put in a heated (120-140degF) drying box for a few days.

Don't make this harder than it really is. I wash such boards in a glass pan with water, then alcohol, then dry in a warm place. This works as long as there are no parts which the water can seep in and cause corrosion problems.

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Mr Yanik, I'm new here but I've had the opportunity to read a few of your very informative posts.

I have a dishwasher, per say, (god, I hope she doesn't read this) so I had to modify your technique using a 409 soaking followed by a scauldingly hot water bath in R/O water followed by anhydrous isopropyl alcohol (for dehydration) followed by a hair drier and then a few hours to sit, low and behold I achieved the desired result. I must say I'm astounded that the phantom resistors have been excorcised completely. Hats off to you Mr. Yanick! Many thanks to Andreas too!

There was a faint smell of what smelled like bleach as I was giving the board the hot water bath, the smell of chlorine being released from a compound perhaps? Or more likely being released from being trapped. I don't think it was a neutralization process because I wouldn't have smelled anything. Anyways, the process works. Thanks, Mike

Well Mike, looks you have got it. Looks like chlorine components. As I can see Jim Yanik has given the information too. May be in your case simply rinsing and brushing with warm (100 F) clear water would help. But I recommend you use calgonite (Jims proposal) or at least boil the water half an hour (minimum) to get rid of the chlorine -- as far as I can remember my holidays in Amerika, all drinkwater is heavily desinfected with chlorine. If you have a local highschool, just contact the chmeistry teachers. They should have/be able to advise too.

Don't worry about the dishwater and your spouse. simply give her your creditcard and send her for shopping. This will take her an houer, and that's enough time for the rinse of the boards.

nice collection you have started. May be you are interested to look at the vitual Tektronix museums, par ex. :

just to name a few.

I personaly prefer use the 2215/2235. Lightweight, reliable, robust. And if I need more bandwith, a couple 2465/A/B are all handy. After 25 years of scope collection, my wife doesn't groan when I use the dishwasher ;-))

ciao, Andreas

Give her the credit card? I'd rather have her read the dishwasher wisecrack. LOL... Uh oh, now I'm in real trouble. I just can't win. LOL

You're right about our H2O here, its chlorinated something fierce. Think'n ahead, I used charcoal treated reverse osmosis "R/O" water for the board bath (no chlorine content) and it tastes great too. I'm gonna peek into Calgonite to see what compounds they use.

I had an opportunity to view the museums you linked to, very nice indeed. What a great time it was when most everything was built to last, and the craftsmanship was exquisite. Thanks again, Mike